Metal beverage cans are designed and manufactured to withstand high internal pressure—typically 90 or 100 psi. Can bodies are commonly formed from a metal blank that is first drawn into a cup. The bottom of the cup is formed into a dome and a standing ring, and the sides of the cup are ironed to a desired can wall thickness and height. After the can is filled, a can end is placed onto the open can end and affixed with a seaming process.
It has been the conventional practice to reduce the diameter at the top of the can to reduce the weight of the can end in a process referred to as necking. Cans may be necked in a “spin necking” process in which cans are rotated with rollers that reduce the diameter of the neck. Most cans are necked in a “die necking” process in which cans are longitudinally pushed into dies to gently reduce the neck diameter over several stages. For example, reducing the diameter of a can neck from a conventional body diameter of 2 11/16th inches to 2 6/16th inches (that is, from a 211 to a 206 size) often requires multiple stages, often 14.
Each of the necking stages typically includes a main turret shaft that carries a starwheel for holding the can bodies, a die assembly that includes the tooling for reducing the diameter of the open end of the can, and a pusher ram to push the can into the die tooling. Each necking stage also typically includes a transfer starwheel to transfer cans between turret starwheels. Often, a waxer station is positioned at the inlet of the necking stages, and a bottom reforming station, a flanging station and a light testing station are positioned at the outlet of the necking stages.
The waxer station is positioned at the inlet of the necking stages and coats an open end of can bodies with a lubricant to prepare the can bodies for necking. Typical waxer stations include a starwheel mounted on a rotating shaft and having a plurality of pockets (for example 12 pockets is common) formed therein. Each pocket is adapted to receive a can body from an input chute as the starwheel rotates. Each pocket typically includes two can rollers that rotate the can bodies as the starwheel rotates. Thus, the can bodies rotate within each pocket as the starwheel rotates. Such rotation allows the entire open end of each can body to be lubricated as the can bodies pass a lubricating station.
To rotate the can bodies, each can roller includes a gear that meshes with gear teeth extending from a housing positioned proximate to the starwheel. As the starwheel rotates, the gears of the can rollers engage the gear teeth of the housing thereby causing the can rollers to rotate.
During the waxing process, debris may be lodged between the gear teeth of the can rollers and housing. As a result, the gear teeth may fracture, thus requiring an operator to either change the gears of every can roller or change the housing. Such tasks are time consuming and may be costly to the manufacturer.